diff --git a/api.go b/api.go
index fe5723365..8e7fa7b2b 100644
--- a/api.go
+++ b/api.go
@@ -2692,9 +2692,9 @@ func mergeIDLists(dst []uint64, src []uint64) []uint64 {
 		return dst[i] < dst[j]
 	})
 	// dedup.
-	n := 0
+	n := 1
 	prev := dst[0]
-	for i := 0; i < len(dst); i++ {
+	for i := 1; i < len(dst); i++ {
 		if dst[i] != prev {
 			dst[n] = dst[i]
 			n++
@@ -2712,9 +2712,9 @@ func mergeKeyLists(dst []string, src []string) []string {
 		return dst[i] < dst[j]
 	})
 	// dedup.
-	n := 0
+	n := 1
 	prev := dst[0]
-	for i := 0; i < len(dst); i++ {
+	for i := 1; i < len(dst); i++ {
 		if dst[i] != prev {
 			dst[n] = dst[i]
 			n++
diff --git a/api_test.go b/api_test.go
index e4826374f..50a59a03e 100644
--- a/api_test.go
+++ b/api_test.go
@@ -860,7 +860,13 @@ type mutexCheckField struct {
 }
 
 func TestAPI_MutexCheck(t *testing.T) {
-	c := test.MustRunCluster(t, 3)
+	c := test.MustNewCluster(t, 3)
+	for _, c := range c.Nodes {
+		c.Config.Cluster.ReplicaN = 2
+	}
+	if err := c.Start(); err != nil {
+		t.Fatalf("starting cluster: %v", err)
+	}
 	defer c.Close()
 
 	m0 := c.GetNode(0)